Selective etching of chalcogenides and its application for fabrication of diffractive optical elements

Abstract

Bulk samples of As and Ge based chalcogenides were synthesized from high purity elements, and thin layers (thickness d≈100–5000 nm) were deposited by vacuum thermal evaporation and/or spin coating. Photoinduced structural changes were studied by Raman and IR spectroscopy. The kinetics of dissolution of thin layers in aqueous and non-aqueous alkaline solvents were studied. Both, positive and negative selective etching behaviours were found and used for production of diffractive optical elements (DOEs). Exposure with a halogen lamp through a Cr mask, classical holographical exposure using an Ar+ laser, and direct writing laser lithography using a He–Cd laser were used to produce amplitude/phase DOEs with feature sizes of 0.37–4 μm. Prepared low efficiency and low lifetime amplitude/phase type DOEs were transformed into corrugated relief type phase DOEs by subsequent selective etching. Positive and/or negative copies of the pattern were obtained depending on the thin layer composition, its prehistory and the applied etching bath. The profiles of the structures produced by etching were subsequently investigated using AFM and REM techniques and basic performance parameters of formed DOE were measured and compared with theoretically calculated values.